1. Field of the Invention
The present invention generally relates to position indicators for buried valves. More specifically, the present invention relates to position indicators that directly relate a position of a valve element, such as a butterfly, plug or the like, of a valve that is buried in the ground.
2. Description of the Related Art
Various types of valves are designed to be buried in the ground. These valves can be used to stop or otherwise control the flow of materials through subterranean pipelines and the like.
One type of valve is considered a quarter-turn valve. There are a number of different versions of the quarter-turn valve, including but not limited to plug valves, ball valves and the like. A quarter-turn valve is so named because the element that controls flow turns one quarter of a revolution between its full open position and its full closed position.
Some quarter-turn valves are very large and heavy. Thus, multiple turn actuators are coupled to the valves through suitable linkages or gear trains. The actuators can be manual actuators or mechanized actuators. In some cases, a hand wheel is mounted to an elongated shaft. The elongated shaft rotates a worm gear at its lower end. The worm gear is positioned in a gear box. The worm gear rotates a gear that is coupled to a valve shaft. The valve shaft is fixed to the element of the valve that occludes or opens the flow passage through the valve. Depending upon the worm gear and gear combination, tens or hundreds of turns of the hand wheel can be required to move the valve element through its quarter-turn sweep.
In many cases, the relative position of the valve element is determined either by counting the number of times the hand wheel is turned or, even more often, simply by the sensory feedback of the field operator. Both of these alternatives can easily lead to catastrophic valve failure. For instance, if the operator loses count of the rotations, which can sometimes number in the hundreds, the operator may damage the valve. Similarly, if the valve operates harder than normal for some reason, the operator may not realize that the valve has not been fully opened and the operator then may damage the valve during a subsequent closing.
To address these concerns, a valve position indicator was previously developed in which an indicator dial was mounted to the elongated shaft that connects the hand wheel to the gear box. Through the use of gearing connected near the actuator (e.g., the hand wheel), the several rotations of the elongated shaft could be translated into movement of an indicator dial from an open indicator position to a closed indicator position.
While this indicator was functional, it had a few drawbacks. For instance, if the gearing broke on the indicator, the indicator would fail to provide a reading. More critically, if part of the drive used on the manual actuator (e.g., the elongated shaft, the worm gear, the gear or the valve shaft) failed, the elongated shaft would continue turning and this would cause movement of the indicator dial, thereby providing a false indication of the valve element position when the breakage occurred.
Some valve and actuator combinations that were designed for above ground use featured a valve element position indicator that was directly coupled to the valve shaft. These indicators would turn through a quarter turn as the valve shaft and the associated valve element turned through its quarter turn. The indicator could take the form of a short tab that was mounted to sweep over a small region on a housing of the actuator. While these indicators were suitable for above ground use, these indicators could not be read in most subterranean applications.